1. Field of the Invention
The present invention relates to a lightning arrestor insulator having a lightning absorber portion consisting a ZnO element and a discharge gap portion both built in a body of the insulator, and a method of producing the same.
2. Related Art Statement
Heretofore, a lightning arrestor insulator having a lightning absorber portion consisting of a ZnO element and a discharge gap portion both built in a body of the insulator has been known, wherein the discharge gap portion performs discharging at a voltage sufficiently lower than an insulative ensurance of a transformer or a so-called cut-out apparatus to be protected to let off the lightning current to the earth so as to protect the transformer or the like at the time lightning occurs and the ZnO element functions to restore instantaneously the electrical insulation of the gap portion to interrupt the electric current flow after the discharging of the discharge gap portion.
An example of such a lightning arrestor insulator is disclosed in Japanese Utility Model Application Publication No. 52-17,719, wherein the gap portion and the ZnO element are arranged in the insulator body, and the insulator body is capped by a ceramic cap by threading or an O-ring.
However, the lightning arrestor insulator of the Japanese Utility Model Application Publication No. 52-17,719 connects the inside arrangements by mere mechanical means, so that it has a drawback in that, if an air-tight sealing of the ceramic cap is broken, the inside of the insulator body is humidized to incur accidents in a power distribution line at a normal working voltage, particularly due to hygromeration of the discharge gap portion.
Heretofore, a lightning arrestor insulator also has been used having a lightning arrestor function of firmly gripping a power supply line and decreasing accidents in the power supply line at the time of a direct hit by lightning.
An example of such an insulator and a method of producing the same is disclosed in applicants' Japanese Patent Application Laid-Open No. 57-160,555, wherein the ZnO element, which protects the insulator per se from an excessively large electric current at the time lightning hits, is integrally fixed and sealed in the inside of the insulator by means of an inorganic glass. The insulator has a characteristic feature of superior airtight sealing and electric insulation properties.
However, in the method of producing the above insulator, the entire insulator is heated and retained in a large homogeneous heating furnace such as an electric furnace, while casting an inorganic glass thereinto, so that production efficiency is bad and an annealing process and other processes are necessary after casting of the inorganic glass in the insulator. Therefore, the production method requires a large furnace and a long time for the sealing, and cannot produce insulators efficiently because a number of insulators that can be produced in the furnace in one sealing operation is restricted by an inner volume of the furnace.